There are known high precision and wide-band impedance- (or more generally electric network) analyzers (e.g. E4990A Impedance Analyzer of Keysight Inc). These devices have large dimensions, they are bulky, expensive and the analysis of the impedance of the electric networks or other parameters is time consuming by this device.
One way to greatly simplify the solution is to use in the analysis instead of the sinewave-based (“harmonic”) excitation signal a simple binary (rectangular) or other approximated by steps signals (M. Min, et al, “Rectangular wave excitation in Wideband bioimpedance spectroscopy,” IEEE International Workshop on the Medical Measurements and Applications, pp. 268-271, May 29-30, 2009). This solution has the disadvantage, that such signal has a very broad frequency spectra—with additional to the main frequency other harmonics, which in turn during the sampling process of the response signal causes due to alias-frequencies (as combinations of multiples of sampling rate frequencies and all frequency components of the measurement signal) significant errors in the analysis of the signal and consequently of the object under test. To reduce such error for such bipolar pulsed excitation signal it has been proposed in the U.S. Pat. No. 7,706,872 to equate to zero certain parts of the signal (so-called pulse shortening). This solution reduces only partially the error of analysis because it allows compensate only for a very small number of harmonics and possible alias-frequencies.
There is known a solution (Kubendran R. et al, “Error Correction Algorithm for High Accuracy bio-impedance measurement in Wearable Healthcare Applications”, IEEE Trans Biomed Circuits Syst. 2014, 8 (2): 196-205), which carries out the analysis of the error estimation and correction based on the equivalent circuit diagram of the measured object. The disadvantage of this solution is that the used simple pulsed (rectangular) signal comprises only one fundamental frequency and its integer harmonics with decreasing amplitudes that does not allow any use of the predetermined spectra of the excitation signal. This narrows significantly the usage of the device and accuracy of the analysis. Also, such solution is based only on one possible equivalent circuit diagram, which does not allow analyzing different circuits. A partial solution could also be adding of the high-order analog low-pass filter to the path of the response signal, to limit the frequency spectra of the response signal to the half of the sampling rate and so avoid the aliasing effect (T. Floyd, “Digital Fundamentals”, 2008, 12). However, such solution increases the price, complexity and adds (mainly linear) distortions and inaccuracies into the signal path, and thus to the analyzing process.
The closest solution is disclosed in the patent EE05668B1 (published also as US2013054178), where sophisticated binary excitations signal is generated, wherein the waveform (pattern) of the signal can be selected according to the desired spectrum. Thus, it is possible to reduce the impact of aliasing frequencies. However, since pulsed signal having infinite spectra is used, which in addition to the desired frequencies contains also a lot of harmonic components and so significant errors occur during the sampling and analysis of the response signal.